An attacker blew himself up after throwing an explosive device into the US embassy compound in Podgorica, the Montenegrin government said Thursday.

Authorities in Podgorica have not released any theories as to the motive for the attack.

"In front of the @USEmbassyMNE building in #Podgorica, #Montenegro an unknown person committed suicide with an explosive device. Immediately before, that person threw an explosive device," the government tweeted, saying the device was "most probably" a hand grenade.

A US State Department spokesperson confirmed "a small explosion near the US Embassy compound" saying officials were "working closely with police to identify the assailant(s)".

A guard at the sports centre who asked not to be named said he "heard two explosions, one after another".

On its Twitter account, the embassy said it had cancelled all visa services for Thursday, adding that access for US citizens "will be available today on an emergency basis".

At 00:30, in front of the @USEmbassyMNE building in #Podgorica, #Montenegro an unknown person committed suicide with an explosive device. Immediately before, that person threw an explosive device from the intersection near the Sport Center into the US Embassy compound. (1 of 2)